1. Field of the Invention
The present invention relates to a load decentralization method and an apparatus thereof, and more particularly, a load decentralization method and an apparatus thereof for decentralizing load centralized to a mobility anchor point (MAP) in a network.
2. Description of the Related Art
In recent years and continuing, mobile IP is proposed for achieving transfer of packets to a location of a mobile node (MN) even in a case where the mobile node has moved in an IP (Internet Protocol) network, and thus enabling movement management of the mobile node within a carrier network regardless of the type of access system.
With mobile IP, the mobile node has a home address which does not change even when the mobile node moves, and a CoA (Care of Address) which changes in correspondence with the movement of the mobile node. By transferring the packets destined (addressed) to the home address of the mobile node, mobile communications in the IP level can be achieved.
Furthermore, a moving Internet user can be accommodated with continuous IP communication, regardless of the type of mobile node that the user is using, by registering the unchanging home address as an ID on the Internet. Particularly, in a case where the user uses a hierarchical mobile IPv6 (Internet Protocol version 6) as the ID, constant two-way IP communication can be attained.
A hierarchical mobile IPv6 technology is proposed as a method for reducing load of the entire mobile IP network by dividing a network into plural hierarchical domains and locally managing the local movement of the mobile node (See IETF Draft draft-ietf-mobileip-hmipv6-05.txt). In the hierarchical mobile Ipv6, a hierarchical node, being referred to as a MAP (Mobility Anchor Point), is disposed in each hierarchical domain.
In hierarchical mobile IPv6, packets to the mobile nodes are specified to pass through the MAP, in which the MAP processes a large load for decapsulating, capsulating, and forwarding all packets destined to the mobile nodes in the hierarchical network.
Furthermore, from the aspect of network management, the hierarchical mobile IPv6 is effective security-wise since the address in the hierarchical network can be hidden. However, during route optimization, the route of constantly passing through the MAP may not necessarily be the optimum route since the address sent to a CN (Correspondent Node) is an RCoA (Regional CoA).
FIG. 1 shows a configuration of a hierarchical mobile IPv6 network. In FIG. 1, mobile nodes denoted as numerals 11, 12, and 13 are CNs (Correspondent Nodes) from the view point of MNs (Mobile Nodes) 26, 27 and 28. The home agent (Home Agent) 15 stores a correspondence between a home address, being an effective address in the hierarchical domain of the mobile node that does not change by the movement of the mobile node within the hierarchical domain, and the RCoa, being an address that changes whenever the mobile node moves overstriding the hierarchies, thereby allowing packets addressed to the mobile node to be transferred to the present location of the mobile node.
The MAPs 17 and 19 each serve as a home agent within the hierarchical domain. Access routers 21, 22, 23, and 24 are gateways for allowing the mobile nodes 26, 27 and 28 to access to the hierarchical mobile IPv6.
Here, a network where the mobile nodes 26, 27 and 28 originally belong to is referred to as a home network (a network at which the home agent storing the home addresses of the mobile nodes 26, 27 and 28 is located). A network where the mobile nodes 26, 27 and 28 perform communication at a portion separated from the home network is referred to as a roaming network. A network interposed between the home network and the roaming network is referred to as a relay network. With the above-described configuration of the hierarchical mobile IPv6 network, the dividing of the network in hierarchical domains, that is, dividing into hierarchical domains of the home network and the roaming network is mainly to apply to the roaming network.
FIG. 2 shows a mobile node registration operation without route optimization in a hierarchical mobile IPv6. Here, the RCoA (Regional CoA) is a virtual IP address, being connected to a link of the MAP, addressed to the mobile node. The RCoA is an IP address that can be received by the MAP and is assigned to each mobile node by the MAP. Furthermore, a LCoA (on-link CoA or Local CoA) is an IP address presently used by the mobile node and is assigned to each mobile node by an access router. The LCoA is updated along with the movement of the mobile node.
In moving within the hierarchical domain, the mobile node 26 reports the LCoA to the MAP 17 during location registration. In moving from one hierarchical domain to another, the mobile node 26 reports the LCoA to the MAP 17 and reports the RCoA to the home agent 15.
FIG. 3 shows a mobile node registration operation with route optimization in a hierarchical mobile IPv6. In a case of obtaining an optimized transfer route for packets transferred from a correspondent node (CN) 11, the mobile node 26 reports the RCoA in manner similar to registering location to the home agent.
FIG. 4 shows packet transfer after the mobile node registration without route optimization in a hierarchical mobile IPv6. In a case where there is no route optimization, since the correspondent nodes 11, 12 and 13 respectively transmit packets to the mobile nodes 26, 27 and 28 to the home address of the mobile nodes 26, 27 and 28, the packets addressed to the mobile nodes 26, 27 and 28 are always transferred via the home agent 15.
FIG. 5 shows packet transfer after the mobile node registration with route optimization in a hierarchical mobile IPv6. In a case where there is route optimization, since the correspondent nodes 11, 12 and 13 respectively transmit packets to the mobile nodes 26, 27 and 28 to the RCoA of the mobile nodes 26, 27 and 28, the packets addressed to the mobile nodes 26, 27 and 28 are not transferred via the home agent 15, but are transferred directly via the MAP 17.
For example, Japanese Laid-Open Patent Application No. 2002-190770 shows a relay apparatus provided with a communication channel in connection with another relay apparatus in which the relay apparatus measures a call amount of a wireless communication apparatus connected thereto, generates a call amount exceed report for reporting exceeding of a total call amount when the call amount exceeds a predetermined value, and transmits the report to the other relay apparatus. The other relay apparatus assigns a portion of relay capacity for securing auxiliary calls for the exceeding call amount and reports this to the relay apparatus with the exceeding call amounts. The relay apparatus receiving the report reports to the mobile node to change connection to the other relay apparatus.
With the static arrangement of the MAP in the hierarchical mobile Ipv6, there is a possibility of being unable to handle dynamically changing internet traffic. Particularly, in a case where the size of a hierarchic domain is large or a case where re-transmission of lost data is frequently performed, there is a problem that a load is frequently concentrated to a particular MAP.
Furthermore, with reference to FIG. 6, in a case of communicating between mobile nodes 26, 26 of different hierarchical domains where one of or both MAPs 17, 19 is in a state of congestion, the MAP (in this example MAP 17), which has already once transmitted data, is required to re-transmit the data when a re-transmission timer is cut off, thereby resulting in further congestion of the MAP 17.